Ballistics test question on an AR-15

[Hi_Powrd_Raine]

I am reviewing a case for a class in school. I am intentionally leaving out specific identifying markers for this case because I am searching for facts instead of hearsay. I would love to hear your opinions. All the facts are listed below:
In an event in 1975, an AR-15 was used to kill, execution-style 2 individuals. This weapon was then moved with other weapons and explosives by other perpetrators in a station wagon. However, due to storing the weapons and explosives too close to the exhaust system the car exploded in a ball of flames, says authorities. The AR-15 was recovered, but the ballistics expert could not perform the firing pin test because the damage to the rifle was extensive; however, an extractor test was done and found to be compatible with casings found near the bodies.
My thoughts are:
>>Being former EOD, I find the "storing too close to the exhaust to be highly unlike to cause an explosion of fire.
>>If the weapon was damaged too much for a firing pin test, wouldn't it stand to prove that it was also damaged for the extractor test?
>>How long does it take to change out parts on an AR-15?
>>There was no conclusive tests that the AR-15 tested belonged to the perpetrator.
>>The situation was during a "war-like" period in that area and everyone walked around heavily armed. It could be possible that the ammo could have been chambered, then extracted, and loaded into another weapon. This could leave the marks of the original weapon on the casing.

I would love to hear your thoughts.

 

[rkh]

It sounds like a contrived hypothetical.

Don't get too wrapped up in the details. The exercise is probably directed to something totally unrelated to EOD or ballistics testing.

 

[Tom C.]

>>Being former EOD, I find the "storing too close to the exhaust to be highly unlike to cause an explosion of fire.

If you are storing explosives under the hood, on the exhaust manifold, perhaps this could happen. I would think it more likely someone torched the car to destroy evidence.


>>If the weapon was damaged too much for a firing pin test, wouldn't it stand to prove that it was also damaged for the extractor test?

If the weapon was too damaged for a barrel or firing pin test, I would think it was too damaged for an extractor comparison. Extractor comparison seems the least reliable comparison test.


>>How long does it take to change out parts on an AR-15?

AR-15 is a military rifle and designed for quick, easy disassembly. Changing out parts should be very fast.


>>There was no conclusive tests that the AR-15 tested belonged to the perpetrator.

Sounds like the cops have no case.


>>The situation was during a "war-like" period in that area and everyone walked around heavily armed. It could be possible that the ammo could have been chambered, then extracted, and loaded into another weapon. This could leave the marks of the original weapon on the casing.

Possible, but seems to me unlikely. More likely that many AR-15s have sufficiently similar extractors as to leave marks indistinguishable among multiple guns.

 

[everallm]

Unless the explosives were "home-brew" or the individuals pre-packed them with thermally sensitive detonators then probability of explosion very, very low.

As for the firing pin/extractor, I can see a theoretical situation where the extractor could be sheared off the bolt, but the firing pin is housed recessed inside the bolt providing it a lot of extra protection.

Extractor dead, firing pin OK YES
Firing pin dead, extractor OK NO

If this was a weapon such as the Sterling machine gun with a fixed protruding firing pin I could imagine such a situation, not on an AR.

It is possible to perform a forensic review and differentiate the pin and extractor it is however mariginal at best unless there is noticeable and unique wear on both.
Oh and if there were any reloaded/re-assembled brass in the batch then extractor marks from more than one weapon would be noted on the case.

 

[trueblue1776]

>>Being former EOD, I find the "storing too close to the exhaust to be highly unlike to cause an explosion of fire.

Agreed, I know of nothing, including Nit. Gly., that would go from exhaust

>>If the weapon was damaged too much for a firing pin test, wouldn't it stand to prove that it was also damaged for the extractor test?

Agree with above, the pin is housed inside the hardest part of the gun, the extractor is on the outside of that part.

>>How long does it take to change out parts on an AR-15?

For an extractor, 15 min, if you include finding my tools, I'm slow compared to more experienced guys.

>>There was no conclusive tests that the AR-15 tested belonged to the perpetrator.

How could there be? especially in a live and fluid combat zone?

>>The situation was during a "war-like" period in that area and everyone walked around heavily armed. It could be possible that the ammo could have been chambered, then extracted, and loaded into another weapon. This could leave the marks of the original weapon on the casing.

Possible, but unlikely. More likely is that almost all Mil-Spec extractors leave nearly the same mark.

What would be a great test, would be to take 20 rounds of .223 to a busy range on Sat. and have everybody with an AR-15 chamber one of your rounds. See if the extractor marks from 20 different guns are clearly distinguishable. I bet they won't be.

 

[ugaarguy]

For an extractor, 15 min, if you include finding my tools, I'm slow compared to more experienced guys.

Trueblue, here's the way a Marine taught me to remove the extractor for detail cleaning. Do the normal Bolt/Carrier/Firing Pin field strip. Grab the bolt and push on the back of the extractor to relieve the spring tension on the extractor pin. Grab your firing pin and push the extractor pin out - pull it out with your fingers if it wont drop out - then carefully take your thumb off the exractor so the spring doesn't go flying. Beats looking for tools .

So, HPR, using the above method you could remove and replace an extractor in under a minute. ARs break down very easily.

 

[trueblue1776]

nice, thanks

 

[stolivar]

American Indian rights activist Leonard Peltier

You are talking about Leonard Peltier for shooting two FBI agents at pine ridge indian reservation in South Dakota.

FBI ballistics expert stating that the gun alleged to have been Peltier's contained a "different firing pin" than that used in the killings. The report was based on tests carried out on bullet casings found at the murder scene. At a district court hearing in 1984 ballistics expert Evan Hodge testified that the teletype referred to other casings found at the scene. But the defense submitted additional evidence showing that Peltier's alleged gun had been eliminated as the murder weapon.

On September 10, 1975, a station wagon blew up on the Kansas Turnpike near Wichita, and a burned-up AR-15 was recovered, along with Agent Coler's .308 rifle. The car was loaded with weapons and explosives which were apparently accidentally ignited when placed too close to a hole in the exhaust pipe. Present in the car among others were Robert Robideau, Norman Charles, and Michael Anderson, said to be associates of Peltier.


steve

 

[Grump]

It could be possible that the ammo could have been chambered, then extracted, and loaded into another weapon. This could leave the marks of the original weapon on the casing.

IME, the firing cycle is needed to put recognizable extractor marks on a brass case.

You ARE talking the extractor mark from extracting, right? I ID rounds from two different .223 rifles that way...

If just being chambered and removed, there's only the snapover mark, which would be "consistent" with every other AR-15*. To get extractor "pull" marks, you would need a dirty chamber and/or ammo with gunk or burrs or dents or something to jam in in there.

*If one has a dimensional anomaly making the snapover mark notably longer or shorter than typical, THEN you could ID it or at least rule one "out". But the only case marks from firing which I believe could be used to ID a specific rifle like bore signatures would be *if* there was a unique scratch pattern on the boltface which is picked up by the primer.

 

[blackhawk2000]

I could change the firing pin, and extractor in about 2 minutes tops, and have the gun back up and running. Or I could swap out any bolt in about 30 seconds. Or I could swap out another upper, in the same time.

What kind of explosives? I can't imagine anything somewhat stable blowing from exhaust heat inside a vehicle. Sounds more like trying to cover tracks.